Gregory J. Mazzaro

• Doctor of Philosophy, Electrical Engineering
• Professor (Full) at The Citadel

An extensive review of nonlinear radar systems is performed. Emphasis is placed on designs relevant to detecting RF electronics that were not intentionally manufactured as visible radar targets. The state of the art in nonlinear radar is conveyed by presenting high-level system architecture, explaining the rationale behind design decisions pertaini...

Multitone harmonic radar is presented. The radar transmits multiple closely-spaced tones and receives nonlinear mixing products as well as harmonics. Harmonic and multitone responses are recorded from commercially-available RF devices. An original method for discriminating between electronic targets, by receiving at least two nonlinear mixing produ...

The long-tail transient responses of a bandpass network to pulsed and switched-tone stimuli are examined and a time-domain closed-form expression of the envelope response is developed. It is shown that the long-tail response leads to interference in frequency-hopping communication systems. Interference, and in particular co-site interference, can r...

RF electronic targets cannot be detected by traditional linear radar because their radar cross sections are much smaller than that of nearby clutter. One technology that is capable of separating RF electronic targets from clutter, however, is nonlinear radar. Presented in this paper is a combination of stepped-frequency ultra-wideband radar with no...

A new waveform processing technique for reducing intermodulation distortion (IMD) generated by an amplitude-modulated signal is presented. The technique eliminates amplifier-generated IMD by time-multiplexing portions of the signal spectrum prior to amplification. The input signal is described as a sum of sinusoidal signals. The peak-to-average rat...

In this work, we design a novel, integrated transmit (TX)/receive (RX) dual-band folded-probe-fed patch (DFPFP) antenna to improve nonlinear radar (NLR) system performance. Designed for down-looking, airborne NLR applications, the DFPFP antenna occupies an improved form factor ( $0.9\lambda \times 0.9\lambda \times 0.1\lambda $ , 1.8 kg) over exis...

p>In this work, a set of custom folded-probe-fed patch (FPFP) antennas are designed to improve the performance of a nonlinear radar (NLR) system. To improve system performance, the custom antennas are designed to have high gain, relatively narrow bandwidth, good linearity, and good size, weight, and power (SWaP) performance. Two FPFP antennas are b...

p>In this work, a set of custom folded-probe-fed patch (FPFP) antennas are designed to improve the performance of a nonlinear radar (NLR) system. To improve system performance, the custom antennas are designed to have high gain, relatively narrow bandwidth, good linearity, and good size, weight, and power (SWaP) performance. Two FPFP antennas are b...

A commonly-offered senior elective for electrical-engineering majors is Antennas & Propagation. The course exposes students to antenna design and radio-frequency (RF) circuit analysis; unfortunately, opportunities to engage in hands-on laboratory work are limited, as equipment required to prototype RF circuits is often prohibitively expensive. Pres...

Data about users is collected constantly by phones, cameras, Internet websites, and others. The advent of so-called ‘Smart Things’ now enable ever-more sensitive data to be collected inside that most private of spaces: the home. The first step in helping users regain control of their information (inside their home) is to alert them to the presence...

Carrier modulation, a variant of intermodulation distortion, is described and exploited for the remote detection of radio-frequency (RF) electronics. To generate carrier modulation, a single frequency illuminates an electronic device, which is actively transmitting, and mixing of the applied probe tone with the device's emission produces intermodul...

A novel technique for exciting radar targets with acoustic and electromagnetic (EM) energy simultaneously is presented. The technique exploits the interaction between the two forms of energy at the target, in a well-controlled acoustic and EM environment, to evaluate the feasibility of standoff acoustic-radar detection of each target. Data recorded...

Radio frequency (RF) circuit elements that are traditionally considered to be linear frequently exhibit nonlinear properties that affect the intended operation of many other RF systems. Devices such as RF connectors, antennas, attenuators, resistors, and dissimilar metal junctions generate nonlinear distortion that degrades primary RF system perfor...

Acoustic-electromagnetic (EM) interaction is evaluated for metallic and electronic target detection. The transmitter consists of a radar-wave generator emitting a single EM frequency and an acoustic-wave generator emitting a single acoustic frequency. The EM wave and the acoustic wave interact at the target. The target reradiates a new EM wave, whi...

An extensive review of nonlinear radar systems is performed. Emphasis is placed on designs relevant to detecting RF electronics that were not intentionally manufactured as visible radar targets. The state of the art in nonlinear radar is conveyed by presenting high-level system architecture, explaining the rationale behind design decisions pertaini...

Nonlinear radar has proven to be a viable means of detecting devices that contain electrical nonlinearities. Electrical nonlinearities are present in dissimilar metals, metal to oxide junctions, semiconductors and more. This paper presents a linear and nonlinear synthetic aperture radar (SAR) system capable of imaging linear and nonlinear targets....

Nonlinear radar exploits the difference in frequency between radar waves that illuminate and are reflected from electromagnetically nonlinear targets. Harmonic radar is a special type of nonlinear radar that transmits one or multiple frequencies and listens for frequencies at or near their harmonics. Nonlinear radar differs from traditional linear...

The authors seek to reduce self-generated distortion in the transmitted probe of an intermodulation radar by applying Linearization by Time-Multiplexed Spectrum (LITMUS). In this technical note, an experiment is conducted to select a minimum time-multiplexing rate and an appropriate filter to accomplish LITMUS when transmitting cellular-band freque...

Harmonic radar is an exciting technology for the detection and ranging of nonlinear targets. The advantage of harmonic radar is that it can separate linear clutter from the harmonic target response. Possible disadvantages of harmonic radar include the need for highly sensitive receiver components, which can result in degraded performance in the pre...

The phase responses of nonlinear-radar targets illuminated by stepped frequencies are studied. Data is presented for an experimental radar and two commercial electronic targets at short standoff ranges. The amplitudes and phases of harmonics generated by each target at each frequency are captured over a 100-MHz-wide transmit band. As in the authors...

Last year, we presented the theory behind “instantaneous stepped-frequency, non-linear radar”. We demonstrated through simulation that certain devices (when interrogated by a multi-tone transmit signal) could be expected to produce a multi-tone output signal near harmonics of the transmitted tones. This hypothesized non-linear (multitone) response...

The radar range equation for detecting targets using linear radar has been de�fined and derived many times for many di�fferent applications. The nonlinear radar range equation has been defi�ned in the literature but a step by step derivation is lacking and no experimental validation has been shown. This paper starts with a nonlinear system model an...

To optimize a harmonic radar for the detection of electronic targets, a system designer must select appropriate frequencies, power levels, transceiver components, antennas, and waveforms. This work focuses on one tradeoff for radar design: duty cycle vs. peak power, for the transmit waveform. Single frequency pulses are studied. It is assumed that...

One of the latest challenges being investigated by the US Army Research Laboratory’s (ARL) Electronics and Radio Frequency (E&RF) Division is the development of a radar system that can accurately detect and range an electronically nonlinear target, such as a detonator of an improvised explosive device (IED). Previous nonlinear radar systems detect...

A simultaneous-frequency nonlinear radar is presented for detecting radio frequency electronic targets of interest. The radar transmits 20 frequencies (“tones”) between 890 and 966 MHz, at approximately equal amplitudes and evenly spaced 4 MHz apart. The radar transceiver and the target are connected by coaxial cabling as a hardware simulation of a...

A spectrum sensing technique is described which is used to enhance the performance of harmonic step-frequency radar in the presence of harmful radio frequency (RF) interference (RFI). This technique passively monitors the RF spectrum for subbands of high signal-to-interference-plus-noise ratio (SINR) within a constrained bandwidth of interest. An o...

A new approach for detecting a particular class of moving targets is presented. This method exploits characteristics of specific non-linear targets to both eliminate moving objects that are not of interest and suppress stationary clutter. Details of the underlying physical phenomena are discussed, and the signal processing procedures leveraged by t...

Multi-band antennas are rarely well-matched between feedpoint and transceiver when the antenna bands are separated by more than an octave. Often, multiple antennas, each assigned its own band, are substituted for a single antenna when the frequency ratio is prohibitively large. To realize a common multi-frequency architecture, the antennas and tran...

Radio-frequency (RF) electronic targets, such as man-portable electronics, cannot be detected by traditional linear radar because the radar cross section of those targets is much smaller than that of nearby clutter. One technology that is capable of separating RF electronic targets from naturally-occurring clutter is nonlinear radar. Presented in t...

In a harmonic radar system design, one of the most important components is the filter used to remove the self-generated harmonics by the high-power transmitter power amplifier, which is usually driven close to its 1-dB compression point. The obvious choice for this filter is a low-pass filter. The low-pass filter will be required to attenuate stop...

Researchers have recently developed radar systems capable of exploiting non-linear target responses to precisely locate targets in range. These systems typically achieve the bandwidth necessary for range resolution through transmission of either a stepped-frequency or chirped waveform. The second harmonic of the reflected waveform is then analyzed...

This paper presents synthetic aperture radar (SAR) images of linear and nonlinear targets. Data are collected using a linear/nonlinear step frequency radar. We show that it is indeed possible to produce SAR images using a nonlinear radar. Furthermore, it is shown that the nonlinear radar is able to reduce linear clutter by at least 80 dB compared t...

This report describes a type of nonlinear radar that detects and locates nonlinear (electronic) targets using ultra-wideband transmission and harmonic reception. Data are presented for a successful test of an experimental harmonic radar at transmit frequencies between 700 and 900 MHz and an output power of 2 W. Detection is accomplished by measurin...

Microwave power amplifiers often operate in the nonlinear region to maximize efficiency. However, such operation inevitably produces significant harmonics at the output, thereby degrading the performance of the microwave systems. An automated method for canceling harmonics generated by a power amplifier is presented in this paper. Automated tuning...

In this paper, spectrum sensing techniques are explored for nonlinear radar. These techniques use energy detection to identify an unoccupied receive frequency for nonlinear radar. A frequency is considered unoccupied if it satisfies the following criteria: 1) for a given frequency of interest, its energy must be below a predetermined threshold; 2)...

In order to generate a detectable harmonic-radar response from an electronic device, the required power-on-target is comparable to that observed directly below a cellular base station. Also, the signal emitted from the target is often very weak. This weak signal must not be masked by harmonics generated by the radar itself. Thus, high transmit powe...

An increasingly cluttered electromagnetic environment (EME) is a growing problem for radar systems. This problem is becoming critical as the available frequency spectrum shrinks due to growing wireless communication device usage and changing regulations. A possible solution to these problems is cognitive radar, where the cognitive radar learns from...

The design of high-resolution radars which can operate in theater involves a careful consideration of the radar’s radiated spectrum. While a wide bandwidth yields better target detectability and classification, it can also interfere with other devices and/or violate federal and international communication laws. Under the Army Research Laboratory (A...

Nonlinear radar exploits the electronic response from a target whose reflected frequencies are different from those transmitted. Reception of frequencies that are not part of the transmitted probe distinguishes the received signal from a linear return produced by clutter and indicates the presence of electronics. Presented in this paper is a type o...

A combined-radar transceiver is constructed which enables target ranging in both linear and nonlinear (harmonic) receive modes. The transceiver is constructed using an arbitrary waveform generator as the signal source, a high-speed digitizing oscilloscope as the signal capture device, and commercial off-the-shelf (COTS) components for the radar fro...

In this report, a unique cognitive nonlinear radar (CNR) is introduced. Research and development efforts for the CNR are currently funded by the U.S. Army Research Laboratory (ARL). The CNR adapts to (1) an increasingly cluttered electromagnetic (EM) environment, a growing problem for ground-based and airborne radar systems; (2) multiple targets; a...

An active analog canceller system is implemented to maximize the dynamic range of a two-tone nonlinear measurement, a common test for nonlinear radio frequency behavior. The canceller uses active feedforward cancellation, controlled by a fully automated iterative algorithm. The system enables testing of a variety of nonlinear channels and devices,...

Proper development of ground-penetrating radar (GPR) technology requires a unique understanding of the electromagnetic (EM) properties of targets and background media. Thus, electromagnetic characterization of targets and backgrounds is fundamental to the success or failure of UWB GPR as a threat detection technique. In many cases, threats are buri...

The effect of cold temperature on the dielectric constant of moist soil is studied. Three soil samples are measured at three moisture levels, at temperatures between –30 and +30 °C, and at seven frequencies relevant to ground-penetrating radar. It is found that for dry soil, cold temperatures have little effect on the dielectric constant. Further,...

A method for measuring complex permittivity using ring resonators is presented. The measurement is suitable for ultra-wideband ground-penetrating radar frequencies. The ring-resonator technique is portable, wideband, and can be performed in-situ, without disturbing the dielectric sample. Design equations and physical dimensions are presented for fa...

The performance of ultra-wideband (UWB) radar systems suffers from reflections between frontend components caused by impedance mismatch. The Synchronous Impulse Reconstruction (SIRE) radar built by the U.S. Army Research Laboratory (ARL) is no exception. While most of the radio frequency (RF) energy in each impulse is transmitted by the radar as de...

Researchers at the U.S. Army Research Laboratory (ARL) designed and fabricated the Synchronous Impulse REconstruction (SIRE) radar system in an effort to address fundamental questions about the utilization of low frequency, ultrawideband (UWB) radar. The SIRE system includes a receive array comprising 16 receive channels, and it is capable of opera...

Pulse reflection between front-end components is a common problem for impulse radar systems. Such reflections arise because radio frequency components are rarely impedance-matched over an ultra-wide bandwidth. Any mismatch between components causes a portion of the impulse to reflect within the radar front-end. If the reflection couples into the tr...

Several upgrades have been incorporated into the Ultra Wideband (UWB) Synchronous Impulse Reconstruction (SIRE) radar, which includes (a) Augmented Reality, (b) antenna array mounting structure, (c) electronic switch and electro-mechanical relay, and (d) low noise amplifiers. The purpose of the experiment is to assess UWB SIRE radar upgrades.

The contribution of bandpass filter memory to intermodulation distortion in narrowband amplifier circuits is examined. A method for generating multisines from filtered switched tones is presented, and techniques for measuring an amplifier's IP3 and extracting a filter's passband using these multisines are developed. It is shown that amplified filte...

Foster's canonical form provides a causal bridge between the transfer function representation of the characteristics of a distributed structure and both time-domain and frequency-domain non-linear circuit simulation. It is particularly advantageous in modelling bandpass-like characteristics. In the modelling procedure, a transfer function having Fo...